1. Field of the Invention
The present invention relates to a gear module capable of securely coupling a transmission gear and a output gear.
2. Related Background Art
For such related arts, the arts disclosed in Japanese Patent application Laid Open No. 60-145551 and No. 8-138299 have been known. For example, as shown in FIGS. 7A and 7B, the conventional gear module 20 comprises the gear 21 rotated by a driving force of a driving motor; the lever 22 capable of rotating around a shaft of the gear 21; and the gear 23 which is pivotally fitted to the top of the lever 22 to be engaged with the gear 21. Moreover, the gear module 20 comprises a pair of gears 24 and 25 which are disposed on both sides of the lever 22, respectively, to be selectively engaged with the gear 23.
The rotation direction of the gear 23 is changed in accordance with which gear of the gears 24 and 25 the gear 23 engages with. Specifically, when the gear 23 engages with the gear 24, the gear 23 is allowed to rotate counterclockwise (see FIG. 7A). On the other hand, when the gear 23 engages with the gear 24, the gear 23 is allowed to rotate clockwise (see FIG. 7B). For this reason, in which direction the gear 23 may rotate, a force is applied in the direction where the gears are engaged strongly, and the gear 23 never fails to engage with the gears 24 and 25.
However, the conventional gear module 20 has been forced to reverse the rotation direction of the driving motor every time when engaging of the gear 23 with the gears 24 and 25 is switched, resulting in complexity of the motor control circuit for controlling the rotation of the driving motor. Here, if the driving motor is allowed to rotate only in the designated one direction, the structure of the motor control circuit becomes simple. However, with such structure of the conventional gear module 20, when the driving motor is rotated, for example, so as to rotate the gear 23 clockwise shown in FIG. 7B, a force acts in the direction on contacting of the gears 23 and 24, and accordingly the gears 23 and 24 come off from each other. The gears 23 and 24 come to weakly engage with each other.
Moreover, since the conventional gear module 20 switches the gear by suddenly reversing the rotation of the gear, a large load is applied to each gear, resulting in a low durability (or reliability) of the module 20. Here, when another actuator is provided additionally and the lever 22 is swung by the driving force of this actuator, the load applied on the gear can be reduced. However, according to this method, the lever 22 must be swung in opposition to a pressing force due to engaging of the gears. Therefore, the load applied to the actuator is excessive.